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So, I thought I had the hunger related bioluminescence for my Keplerians figured out. That once the hunger hormone reaches a certain threshold, the hormone receptors on some cells of a bioluminescent organ trigger the activation of a certain fluorescent protein which causes the baby's abdomen to glow. And I figured that an evolutionary reason to evolve bioluminescence would be to warn predators that they are poisonous or to mimic poisonous animals.

In other words, bioluminescence would both be a defense and a hunger cue simultaneously. And I figured that since the glow stops after 6 months of life, that maybe the mother's milk doesn't completely meet the nutritional needs and so it draws the rest of the needed nutrients from the bioluminescent organ, ultimately shrinking it and that in the place of this bioluminescent organ would be a more developed digestive tract and bigger lungs.

However, I got some feedback that the reason for the bioluminescent organ to shrink does not make sense and I got 2 alternatives in that feedback.

Alternative 1: Bioluminescent organ stays into adulthood, but the hormone it responds to changes

This is one of the alternatives that I got. In this alternative, the bioluminescent organ stays, but the hormone receptors on the cells change. So it goes from responding to the hunger hormone to signal that the baby is hungry to responding to adrenaline, the fight or flight hormone, later on in life. This would mean that whenever an adult Keplerian gets significantly stressed out, they would glow to signal to others that they are stressed.

I see a few problems with this though. For one thing, Keplerians are social, so having bioluminescence as a stress cue does not make any sense when vocalizations and physical movements can get across stress just as well on their own. Also, Keplerians have a human-like pregnancy. Pregnancy is going to push on the bioluminescent organ. What if that causes the main artery that supplies the organ with oxygen and nutrients to be partly occluded? That could potentially cause an infarction, especially in a multiple birth pregnancy. And that could lead to a life threatening infection. And pregnancy leads to stress as well, so it could mean an almost constant glow in those who are pregnant. Again, the physical and social changes are enough to know the Keplerian is pregnant, so bioluminescence in response to stress caused by pregnancy doesn't make sense either.

Alternative 2: Bioluminescent organ becomes poison glands

Now, this is what the person giving me feedback said would be a way to make the shrinking of the bioluminescent organ make sense. But, what would be the use of poison glands in an intelligent species? I mean, even as babies, Keplerians have quite a bit of intelligence and they develop mental, social, and physical skills fast. I could see poison glands being viable for say a reptilian species, but a humanoid species with a lot of intelligence? I don't see how both the intelligence and the poison glands would be viable.

So, clearly there are flaws in both proposed alternatives. I think the reason that the person giving feedback said that my original idea doesn't make sense has to do with the mother's milk not quite reaching the nutritional needs. Basically, the person giving me feedback was implying that the mother's milk not quite reaching nutritional needs would cause the Keplerian to have organ failure from autophagy and it would be fatal. But, what if all except the bioluminescent organ has receptors for a certain protective factor that prevents the breakdown of tissues? And what if this protective factor is produced in abundance in the fetus and lingers around for months after birth? That would solve the organ failure issue while also not preventing the bioluminescent organ from shrinking to nothing over 6 months, leaving room for a more developed digestive tract and bigger lungs.

So does my original idea make sense or does one of the proposed alternatives make more sense, despite the flaws I pointed out in both alternatives?

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  • $\begingroup$ What do these critters eat? $\endgroup$ – Joe Bloggs Jan 31 at 10:05
  • $\begingroup$ Reminder to close-voters: The problem cannot be fixed if the OP is not made aware of it. $\endgroup$ – Frostfyre Jan 31 at 17:46
  • $\begingroup$ That being said... I disagree with the existing opinion-based close votes. This question does not rely on opinion to answer. There are three possible answers that require sufficient supporting information to declare that a given option is the best. This is exactly what this is community is here to do. $\endgroup$ – Frostfyre Jan 31 at 17:48
  • $\begingroup$ @JoeBloggs They are omnivores. They eat plants, meat, both muscle and organ meats, and they even eat raw bone, especially when pregnant. $\endgroup$ – Caters Jan 31 at 22:05
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Alternative 1, with the twist: bio-luminescent organ is skin!

Well, not all skin. Belly skin.

Some skin on the belly is different. We are talking hormonal changes which happen during male puberty which allow human males to grow beards and whiskers. On the other hand, you do not grow beard on your feet, do you? Instead of hair follicles growing, you have bio-luminescent cells glowing.

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None of the above

That once the hunger hormone reaches a certain threshold, the hormone receptors on some cells of a bioluminescent organ trigger the activation of a certain fluorescent protein which causes the baby's abdomen to glow. And I figured that an evolutionary reason to evolve bioluminescence would be to warn predators that they are poisonous or to mimic poisonous animals. In other words, bioluminescence would both be a defense and a hunger cue simultaneously.

I'm not so sure that this makes sense. Animals can evolve certain things as a warning, but the poison warning on earth are bright colors, and there's a good reason for this - they're always visible. When a predator sneaks up on a poison dart frog, it can see from behind that the animal is bright red - and therefore not to be eaten. If a predator sneaks up on your Keplerian and the bioluminescence is off, than it does not matter if the Keplerian is poisonous, it is dead. The organ would be perpetually on if it's a poison warning, and that conflicts with the hunger cue aspect of it.

Also, if this is a defensive mechanism, than adult Keplerian would have it on at all times, the organ wouldn't shrink, go away, or turn into anything else.

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A few points on these cool ideas.

In humans the hunger response is actually the "satiety" response and it is not regulated by hormones, but by "stretch receptors." Stretch receptors are part of the nervous system and are connected directly to the brain--no hormones necessary and thus no full-body response necessary. They operate by sending a signal to your brain in response to the mechanical force exerted on the stretch receptors when your stomach is full. Thus, hunger is "the absence of satiety" in us. I dunno if this helps. I will say that if hunger is hormone-controlled, then perhaps your animals REQUIRE a full body response such as temporary changes in their physiology (faster running to catch prey, smooth muscle contractions to allow them to fit larger prey or bones they can chew into their mouths, etc.)

Anyways, since you mentioned mother's milk in addition to poison, consider mammalian milk. It is only digestible by babies, and the only adult organisms that can metabolize lactose are humans--we evolved to do so because its a free way of turning grass into food (via cows). If your Keplerians have a different intestinal flora as infants than they do as adults, then they may be able to digest the mother's milk as infants, but to adults and other animals, who are unable to metabolize whatever unique molecule is in the milk, it is poisonous to them (for example, it rapidly accumulates to toxic levels in their livers). For a simpler example, you could equate it to alcohol toxicity in people with the alcohol dehydrogenase gene, and those without it).

So to answer your question, the use of poison glands is to feed their young! I hope that adds something to your thought process.

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  • $\begingroup$ Then, why does the human body produce grhelin, the hunger hormone and leptin, the "I'm full" hormone, if they aren't necessary? $\endgroup$ – Caters Feb 1 at 19:04
  • $\begingroup$ I'll preface this and retroactively apply this preface to my previous post stating that I'm not a doctor and much of this is based of a few lectures in physiology class a couple years ago at uni. I don't deny my post is flawed, but lets talk through it together and have a discussion. No matter if you're right and I'm wrong. Anyways to the heart of the matter--the role of hormones in hunger. Because you are designing these guys, it's whatever you want. In humans, grhelin looks to be in change of the "macro" scale of hunger (feeling good after eating, keeping a consistent rhythm of meals)... $\endgroup$ – doe Feb 2 at 2:36
  • $\begingroup$ and stretch receptors are responsible for hunger with a very narrow scope, which is "stomach empty, tell brain the body is hungry." It's a simpler pathway which produces a more pronounced response. That's my broad overview of the topic with the information (wikipedia) I have at hand. Let me know what you think and what you are thinking about for the story more! Best, $\endgroup$ – doe Feb 2 at 2:40

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